High-frequency electron discharge



Apnl 21, 1953 N. E. LINDENBLAD Re. 23,647

HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING HAVE TYPE Original Filed June 25, 1947 3 Sheets-Sheet l Rf. INPUT INVENTOR.

m5 7 E; LINDENBLAD ATTORN EY P" 1953 I N. E. LINDENBLAD Re. 23,647

HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPE Original Filed June 25, 1947 3 Sheets-Sheet 2 Fig. 2a

' INVENTOR.

NILS E. LINDENBLAD BY -g E F ATTORNEY I mil/00E Apnl 21, 1953 N. E. LINDENBLAD Re. 23,647 HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPE Original Filed June 25, 1947 3 Sheets-Sheet 3 l/IIE MAGNET/C FIEL?7C0/ Rf. OUTPUT U/IE INVENTOl. T NILS aunneuamn av h ATTORNEY Reiuued Apr. 21, 1953 HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE OF THE TRAVELING WAVE TYPE Nils E. Lindenblad, Princeton, N. 1., asslgnor to Radio Corporation of America, a corporation of Delaware Original No. 2,578,434, dated December 11, 1951, Serial No. 756,851, June 25, 1947. Application for reissue August 19, 1952, Serial No. 305,311

Matter enclosed in heavy brackets l, appears in the original patent butforms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

26 Claims.

An object of the invention is to provide an improved electron discharge device capable of amplifying a wide band of high frequencies and which does not depend upon resonance phenomenon in the output circuit.

Another object is to provide a growing wave (sometimes called a traveling wave) t pe tube having an outer metallic shell or envelope surrounding a helical or spiral line, and which is of such geometric configuration as to gradually change the characteristic impedance of the helical line from a relatively high value in the center of the line to a lower value near the ends of the line.

A further object is to enable the terminals of a helical conductor in a growing wave type tube to match the characteristic impedance of connecting coaxial transmission lines.

A still further object is to provide a wide band helical line type of growing wave amplifier tube for use at high frequencies, which prevents or minimizes the occurrence of parasitics at very high frequencies outside the range of frequencies to be amplified.

A detailed description of the invention follows in conjunction with the drawings, wherein:

Figs. 1, 3 and 4 show three difierent embodiments of the invention, and

Figs. 2a to 2f inclusive show six different types of coupling or impedance transformation circuits which can be used between the terminals of the amplifier tube of the invention and the connecting coaxial transmission lines.

Referring to Fig. l in more detail, there is shown a wide band growing wave amplifier tube of the broad general type described in my U. S. Patent No. 2,300,052, granted October 27, 1942, and in my copending application Serial No. 724,330, filed January 25, 1947, in which a helical conductor surrounds a stream of electrons and is in energy coupling relation thereto. The improved amplifier tube of Fig. 1 comprises a tubular non-magnetic metallic envelope or shell which surrounds a helical conductor ii. A suitable primary cathode 14 is provided at one end of the tube for furnishing a concentrated heavy stream of electrons which pass along a path which extends axially through the interior of the helical conductor ii [and which]. The electron stream is finally collected by a. collector electrode I! at the other end of the tube. This cathode 14 is shown, by way of example, as campus-- ing a cylinder [ll] which has only a portion terial. A repeller electrode l6 at the adjacent to the cathode [end of the tube] serves to repel or concentrate the electrons emitted by the oathode toward the helical conductor II. A magnetic field coil ll surrounds the tube and is energized by a direct current source I! in series with a variable resistor i9. The field coil is so arranged that the lines of flux extend parallel to the [tube in an axial direction] path of the electron stream in order to focus the stream [beam] of electrons along the center of the tube. It should be noted that the repeller electrode l8 ismaintained at a negative potential relative to the cathode, while the collector electrode i2 is maintained at a slight positive potential relative to the cathode. In the construction of the tube, it may be desirable for the collector electrode to be at a slight negative potential relative to the cathode or even at the same potential as the cathode. The metallic envelope I0 is at ground potential which is equivalent to a positive potential with respect to the cathode. A coaxial transmission line it supplies radio frequency input current to one terminal of the helical conductor I i, while the amplified current is abstracted from the other terminal of the helical conductor II by an output coaxial line 20.

In order to assure a vacuum tight shell or envelope l0, glass beads 21 are provided in the input and output coaxial lines at a location near shell Ill. Obviously, the glass beads can be positioned at any suitable location.

The helical conductor ii is a plurality of wavelengths long peripherally along the helix at the center frequency of operation. The input energy supplied to the helix II by input line I! causes the electrons passing through the interior of the helix ii to be bunched. The helix II has such dimensions as to couple properly with the electron stream passing along the axis thereof. In other words, the axial wave velocity along the helix substantially matches the axial velocity of the electron stream passing therethrough.

The characteristic impedance of this helical conductor is of the order of several hundred ohms, whereas the characteristic impedances of the coaxial lines l3 and 20 are each of theorder of 50 ohms. as an example. In order to match the impedances of the coaxial lines i3 and 30 to the characteristic impedance of the helical conductor l I, to prevent the production of standing waves due to reflections at the junction between coaxial lines to which it is connected. In order to taper the impedance of the helical conductor ll down to approximately 50 ohms, which is assumed to be the impedance of the coaxial lines, the distance between the last turn of the coil II and the surrounding tapering shell II should be of the order of the radius of the wire constitutin the coil ll. Because this might be difiicult to achieve in practical conditions due to the very close spacing required. it will sometimes be more convenient not to taper the characteristic impedance of the helical conductor ll down as far as 50 ohms, but rather to a value of the order of 100tol25ohms,inwhichcasethespacingbetween the last turn of the coil I I and the tapering envelope Ill can be larger. In this last case, it is advisable and preferred that a tn line link having tapering impedance be inserted externally of the tube between the last turn of the coil ll andthe50 ohmscoaxialline.

Figs. 2d, 2e and 2! show three difierent arrangements for connecting a transmission line link having tapering impedance between the last turn of the coil II and a 50 ohms coaxial transmission line shown as It in Figs. 2d. 2e and 21'. In Fig. 2d the tn line link or impedance transformer. so to state. is labeled II and has an inner conductor of gradually increasing diameter. It should be noted that the length of the transmission line II is of the order of two wavelengths at the mean operating frequency. The inner conductor of the link II is relatively small at the end connected directly to the coil II and increases in diameter to amaximum at the end connected to the coaxial line II. The gradual change in diametric ratio between the inner and outer conductors of the link ll eifects the impedance transformation. Fig. 2e shows an arrangement equivalent to that of Fig. 2d, the difference being that this link identified as II has the outer conductor changing in diameter rather than the inner conductor. In Fig. 2f

the line link is identified as I!" and has an inner conductor which is coiled and has closer spacing between turns thereof near the helical conductor it than near the coaxial line II. The radius of the spiral may also be made smaller as the pitch increases. The outer conductor diameter may also taper down in this direction. The three arrangements of Figs. 2d, 2e, and 2f are equivalent to each other and show an impedance transformation means for coupling the low impedance coaxial line It to the higher impedance terminal of the helical conductor II.

It should be understood that the arrangements ofFigs.2d,2eand2fmaybeusedatboth terminals oi the helical conductor II, when the characteristic impedance of the helical conductor is not lowered to a point where it exactly matches thatofthecoaxiallinetowhichitisconnected. The ents of Fig.1 as shown, or in combination with coupling circuits of Figs. 2d, 2e and 2f insure substantially perfect impedance match.

ing between the helical conductor II and the input and output lines for all frequencies which can be amplified by the growing wave tube. The helicalcoil ll isdesignedtohaveaslowattenuation as practical without enabling undesired refiectionsalongthecoil ll toproduceparasitics.

frequency carrying groundreturn. Inl'ig.2at hecoaxial shown connected to a folded dipole 3|. shows the coaxial line stub I! connected between the terminal of the helical conductor I l and a sleeve type antenna II. In the arrangements of Figs. 2a to 21' inclusive only those portions of the growing wave amplifier tube of the invention have been shown which are necessary for an understanding of the principles involved. Thus, in these figures the conical tapering end of the metallic shell has been shown and only a few turns of the helical conductor ll near one of its terminals. It will be understood that the remaining portion of the growing wave amplifier tube not shown in these figures may take the form shown in Fig. l, or those of Figs. 3 and 4 described hereinafter.

In constructing the growing wave vacuum tube in accordance with the invention, it is advantageous to provide a coil ll which has no loss at the frequencies to be amplified, so that as much as possible of the kinetic energy of the bunched electrons can he transferred to the working load. At other frequencies, it is of course immaterial whether a loss occurs internally or externally of the tube. The arrangement, however. should be such that sufiicient loss is introduced to prevent parasitic oscillations, and one way that this can be done is by employing external trap circuits or deflecting circuits which will connect artificial loads (damping circuits) to the tube.

Fig. 3 shows an arrangement employing the principles of the invention, wherein parasitics can be prevented at very high frequencies outside the range to be amplified at which the conducting metallic shell ll may provide undesired cavity resonance conditions. This is done by employing reactive impedance elements in the form of absorber resistors. it connected to capacity pickup plates ll. These pick-up plates II are uniformly distributed along at least a substantial portion of the length of the helical conductor II and have such dimensions that their reactance is very h in the operating frequency range but becomes low at frequencies higher than the highest operating frequencies. At these frequencies higher than the operating frequency, the low reactance between the helical conductor II and the capacity pick-up plates will permit sufiicient current to pass into the resistors II to introduce the desired damping efiect to prevent the production of standing waves on the conductor II.

The tube with reactive impedance elements distributed along the helical conductor, as shown in Fig. 3, is claimed in my divisional application Serial No. 229,072, died May 31, 1951.

Fig. 4 shows another embodiment of the invention wherein the growing wave amplifier tube is divided into two chambers one of which can be called an input chamber and the other of which an output chamber. The input chamber' contains a first primary [includes the] cathode 14 and [the] a first helical conductor ll along whose axis the electron [beam] stream from cathode 14 The conductor ll serves to bunch the electrons passing therethrough. [One] The input end of the conductor II is connectedtotheinputcoaxialline ll,whilethe otherendisterminatedbyaresistorll whose 8 value matches the characteristic impedance of the' helix II' at that end.' A suitable metallic partition ill having an aperture il therein serves to separate the two chambers. The output chamber [includes a] contains an annular second primary cathode It [provided with] coarially surrounding the aperture 61, a repeller electrode II, a helical conductor II", and the collector electrode [2. It should be noted that the [terminal] end of the helical conductor l I" which is nearest the partition [ll] 60 is terminated by a resistor 'll of a value equal to the characteristic impedance of the helix II".

the output'coaxial line 20. The repeller electrode ll of the cathode arrangement. in the output chamber is maintained at a. negative potential relative to the cathode 80.

In the operation of the growing wave amplifier tube of Fig. 4 there is obtained [a beam] an electron stream of relatively low electron intensity at the input end of the tube in order to obtain an improved signal-to-noise ratio. High power output, however, requires greater electron [beam] intensity than is provided at the input end of the tube, and this is achieved by the use of the second cathode lli which introduces additional electrons at a location where the inputsignal has been substantially amplified. The electrons from the first and second cathodes add to each other and pass through the interior of the second helix [H'] 11". Electrons passing through the first helix are bunched, and these bunched electrons passing through aperture 6| aid in bunching the electrons from the second cathode which pass through the helix Ii". The procedure indicated in Fig. 4 may of course be repeated, i. e. a second, a third, etc. partition may be introduced.

Although the helical conductor II in Figs. 1.

3 and 4 has been shown as having the same pitch throughout its length, it should be noted that it may be tapered toward the end near the collector electrode in order to slow down the waves on the conductor l l, to maintain substantial synchronism between the waves and the retarded electrons. The potential on the collector electrode will be held at suitable values depending on the speed of the electrons approaching it and may be maintained at a low negative or a small positive potential relative to the cathode. In some cases it may be desired to maintain the helical conductor at a particular potential relative to ground. In such a case the helix can be isolated from the input and output coaxial lines from a direct current standpoint by means of blocking condensers, and the helix supplied with a suitable potential relative to the cathode.

The growing wave amplifier tube of the invention is particularly useful in a radio relaying system in amplifying an extremely wide band of radio frequency waves, and wherein the mean while its other [terminal] or output'end is connected to frequency is of the order of many hundreds or' war'dly as illustrated.

surrounding said helical conductor over sub-- stantially the entire length thereof and spaced therefrom, the diameter of said element measured between oppositely disposed points on said surface increasing from a terminal of said helical conductor to a point intermediate the ends of said helical conductor, to thereby gradually change the characteristic impedance of said helical conductor, and means for coupling said terminal to a. radio frequency circuit.

. 2. An electric tube comprising a helical conductor through the interior of which a stream of charged particles is adapted to pass, a hollow cylindrical element having a metallic surface surrounding said helical conductor over substantially the entire length thereof and spaced therefrom, the diameter of said element measured between oppositely disposed points on said surface increasing from both ends of said helical conductor to spaced points intermediate the ends of said helical conductor, the diameter of said surface between said spaced points being uniform, an input circuit coupled to one end of said helical conductor, and an output circuit coupled to the opposite end of said helical conductor.

3. An electron discharge device comprising a helical conductor, means for projecting a stream of electrons through the lnteriorof said helical conductor. said helical conductor being positioned to be in energy coupling relation to said stream, a metallic shell surrounding said-helical conductor and spaced therefrom, a transmission line having a characteristic impedance different from that of said helical conductor and coupled to said helical conductor, the spacing between said shell and helical conductor gradually decreasing from a point intermediate the ends of said helical conductor to' the junction point of said line and helical conductor. whereby the characteristic impedance of said helical conductor gradually changes over that portion of the length thereof measured from said intermediate point to said junction point.

4. An electron discharge device comprising a helical conductor, means for projecting a stream of electrons through the interior of said helical conductor, said helical conductor being positioned to be in energy coupling relation to said stream, a metallic shell surrounding said helical conductor and spaced therefrom, a transmission line having a characteristic impedance different from that of said helical conductor and coupled to said helical conductor, the diameter of said shell gradually decreasing from a point intermediate the ends of said tube to the junction point of said line and helical conductor, whereby the characteristic impedance of said helical conductor gradually changes over that portion of the length thereof measured from said intermediate point to said junction point.

5. An electron discharge device comprising a helical conductor. a cathode and a collector electrode at opposite ends of said helical conductor, whereby a stream of electrons may pass from said cathode to said collector electrode, said helical conductor being in energy coupling relation to said stream of electrons, a metallic tube positioned coaxially with respect to said helical conductor and spaced therefrom. the spacing between said metallic tube and said helical conto said one terminal.

7 ductor gradually decreasing from a point intermediate the ends of said device toward one end of said helical conductor, whereby the characteristic impedance of said helical conductor gradually changes from said point toward said one end, and a transmission line coupled to said one end of said helical conductor.

6. An electric tube comprising a helical co ductor along the axis of said tube, means for projecting a stream of electrons coaxially with respect to said helical conductor, a hollow cylindrical non-magnetic metallic element also positioned coaxially with respect to said helical conductor and spaced therefrom and extending over substantially the entire length of said helical conductor, the spacing between said cylindrical metallic element and said helical conductor decreasing from a point intermediate the ends of said helical conductor toward one terminal of said helical conductor, whereby the characteristic impedance of said helical conductor changes over that portion of the length thereof meas- 'ured from'said intermediate point toward said one terminal, and a line adapted to carry radio frequency currents coupled to said one terminal. 1'1. An electron discharge device comprising a helical conductor, means for projecting a stream of electrons through the interior of said helical helical "conductor oversubstantially the entire length thereof and spaced therefrom, the spacing between said shell and said helical conductor in- '-crasing from both ends of said helical conductor toward spaced points intermediate the ends of said helical conductor, the diameter of said shell being uniform between said spaced points, means for producing a magneticfield having flux lines running parallel to the 'axis of said helical conductor, and coaxial transmission lines having characteristic impedances different from that of said helical conductor coupled to both ends of said helical conductor.

tallic tube, means for projecting a stream of electrons from one chamber into and through the other chamber, a helical conductor in each of said chambers in energy transfer relation to said stream, the side walls of each chamber being spaced from the helical conductor contained therein, the spacing between the side walls of each chamber and the enclosed-helical conductor being non-uniform and increasing from one terminal of the helical conductor toward a point intermediate the ends of said helical conductor, and a radio frequency carrying medium coupled 10. An electron discharge device comprising first-and second chambers placed longitudinally end-to-end, the side walls of said chambers being constituted by a continuous cylindrical metallic tube, means for projecting a stream of electrons from one chamber into and through the other chamber, a helical conductor in each of said chambers in energy transfer relation to said stream, the side walls of each chamber bein spaced from the helical conductor contained therein, the spacing between the side walls of each chamber and the enclosed helical conductor being non-uniform and increasing from one terminal of the helical conductor toward a point intermediate the ends of said helical conductor, a radio frequency input coaxial line coupled to said one terminal of one helical conductor, and a radio frequency output coaxial line coupled to said one terminal of the other helical conductor.

11. An electron discharge device comprising first and second chambers placed longitudinally end-to-end, an apertured partition between said chambers for enabling electrons to pass therethrough, a cathode near that end of said first chamber farthest removed from said partition, and a cathode in said second chamber at a location near said partition and shielded by said partition from said first cathode, whereby the electrons emanating from the cathode in said second chamber add to the electrons emanating from cohdiictor, a metallic shell surrounding said,

through, a cathode near that end of said chamber farthest removed from said partition, and a cathode in said second chamber at a location near said partition, whereby the electrons emanating from thecathode in said second chamber add to the electrons emanating from.

'said first cathode and passing through said partition, means for focusing the electrons from said cathodes into a stream passing in one general direction, and a helical conductor in each of said chambers positioned to be in energy coupling relation to said stream.

13. An electron discharge device comprising first and second chambers placed longitudinally end-to-end, the side walls of said chambers being constituted by a continuous cylindrical metallic tube, a helical conductor in each of said chambers positioned around the axis thereof, said chambers being separated by an apertured partition for enabling electrons to pass therethrough, a cathode in said first chamber arranged to pass a concentrated stream of electrons through the interior of the helical conductor in said first chamber and through the apertured partition, and a cathode in said second chamber located near said partition for producing additional electrons which add to the electrons from said first chamber for passing through the interior of the helical conductor in said second chamber, said helical conductors being in energy transfer relation to said electron stream, an input circuit coupled to the helical conductor in said first chamber, and an output circuit coupled to the helical conductor in said second chamber.

14. An electron discharge device as defined in claim 9, wherein said means for projecting a stream of electrons includes a cathode in each of said chambers.

15. An electron discharge device adapted to operate over a predetermined frequency range comprising a helical conductor, means for projecting a stream of electrons through the interior of said helical conductor, said helical conductor pedance different from that of said helical conductor and coupled to said helical conductor, the spacing between said shell and helical conductor gradually decreasing from a point intermediate the ends or said helical conductor to the junction ance values of said pick-up elements being relatively high in said operating range of said discharge device and relatively low at frequencies higher than the highest operating frequency of said range.

16. An electric tube comprising a helical conductor eflectively divided into two parts, means for projecting a stream of electrons coaxially with respect to said helical conductor and over substantially the entire length thereof, a hollow metallic shell surrounding said helical conductor and spaced therefrom, the diameter of said shell increasing from opposite ends of said helical conductor to spaced points intermediate said opposite ends, the diameter of said shell between said points being uniform, an input circuit coupled to one end of said helical conductor and an output circuit coupled to the opposite end of said helical conductor.

17. An electron discharge device comprising firstand second chambers placed longitudinally end-to-end, an apertured partition between said chambers for enabling electrons to pass therethrough. a cathode near that end of said first chamber farthest removed from said partition, and a cathode in said second chamber at a cation near said partition and shielded by said partition from said first cathode, whereby the electrons emanating from the cathode in said second chamber add to the electrons emanating from said first chamber and passing through said partition, means for focusing the electrons trom said cathodes into a stream passing in one general direction, and a helical conductor in each of said chambers positioned to be in energy coupling relation to said stream.

18. An electron discharge device comprising an elongated envelope containing means including a first cathode for projecting a first stream of electrons along a given path, means including.

a second cathode positioned along said path for projecting asecond stream of electrons in space-charge-coupling relation to said first stream and in the same general direction, a helical conductor surrounding said path and coupled to at least one of said streams for modulating said stream in accordance with-a signal to be amplified, means coupled directly to both 01 saidstreams in a region beyond said second cathode and said conductor for extracting amplifled signal energy from said streams, and means for collecting said streams.

19. An electron discharge device as in claim 18, in which said energy-extracting means comprises a second helical conductor surroundin said path.

20. An electron discharge device as in claim 19, further including input and output transresistivemeans terminating the other ends of said two conductors.

21. An electron discharge device comprising an elongated envelope containing means including a first primary cathode for projecting a first stream of electrons along a given path, means including a second primary cathode positioned along said path in spaced relation to said first cathode for projecting a second stream of electrons in space-charge-coupling relation to said first stream and in the same general direction, means interposed between said two cathodes and coupled to said first stream only for modulating said stream in accordance with a signal to be amplified, means coupled directly to both of, said streams in a region beyond said second cathode for extracting amplified signal energy from said streams, and means for collecting said streams.

22. An electron discharge device as in claim 21, in which said second cathode is an annular electrode coaxially surrounding said path.

23. An electron discharge device as in claim 21, in which said modulating means comprises a helical conductor surrounding said path.

24. An electron discharge device as in claim 23, in which said energy-extracting means comprises a second helical conductor surrounding said path.

25. An electron discharge device as in claim 24, further including input and output transmission lines coupled to the input and output ends, respectively, of said two conductors, and resistive means terminating the other ends of, said two conductors.

26. An electron discharge device as in claim 25, including conductive shield means surrounding said two helical conductors and to which said resistive means are connected.

NILS E. LINDENBLAD.

References Cited in the file 01' this patent 

